Introduction Patients with clinically suspect arthralgia (CSA) have, according to their rheumatologists, an increased risk of rheumatoid arthritis (RA), but their actual outcome is unexplored. This longitudinal study investigated (1) progression from CSA to clinically detectable arthritis and (2) associations of clinical factors, serological factors (among which are anticitrullinated peptide antibodies (ACPAs)) and MRI-detected subclinical inflammation with arthritis development.

Methods 150 patients with CSA were followed for ≥6 months. At baseline, clinical and serological data were collected and unilateral 1.5 T-MRI of metacarpophalangeal (MCP), wrist and metatarsophalangeal (MTP) joints was made. MRI scoring was done according to the RA MRI scoring system. Subclinical MRI inflammation was defined based on MRI results of 193 symptom-free persons.

Results During follow-up (median=75 weeks, IQR=41–106 weeks), 30 patients developed clinical arthritis; 87% did so <20 weeks after inclusion. In multivariable analyses, age, localisation of initial symptoms in small and large joints (compared with small joints only), C-reactive protein level, ACPA-positivity and subclinical MRI inflammation significantly associated with arthritis development; ACPA and MRI inflammation were most strongly associated (HR (95% CI) respectively, 6.43 (2.57 to 16.05) and 5.07 (1.77 to 14.50)). After 1-year follow-up, 31% of the patients with MRI inflammation and 71% of the ACPA-positive patients with MRI inflammation had progressed to arthritis. Forty-three per cent of the patients that developed arthritis within 1 year were ACPA-negative; 78% of them had subclinical MRI inflammation at baseline. When MRI inflammation was absent arthritis development was infrequent (6% in all patients with CSA and 3% in ACPA-negative patients with CSA).

Conclusions Subclinical MRI inflammation precedes clinical arthritis with a few months. Subclinical MRI inflammation is, independent of other factors such as ACPA, associated with arthritis development.